1. Field of the Invention
This invention relates to oxidation and/or ammoxidation catalysts containing the elements iron and molybdenum in a catalytically active oxidized state and to a process for preparing such catalysts, which catalysts exhibit an improvement in selectivity and yield. In another aspect, this invention relates to a process for employing such catalysts to effect the oxidation and/or ammoxidation of alcohols. In a more specific aspect, this invention relates to a process for employing such catalysts for the ammoxidation of methanol to hydrogen cyanide.
It is known that methanol can be oxidized to the corresponding carbonyl compounds, formaldehyde and formic acid. It is also known that methanol can be ammoxidized to hydrogen cyanide (methanenitrile). The value of such carbonyl compounds and hydrogen cyanide is generally well recognized, with hydrogen cyanide being one of the most valuable compounds available to the chemical industry. Its chief commercial use is as a basic chemical building block for such chemical products as sodium cyanide, potassium cyanide, methyl methacrylate, methionine, triazines, iron cyanides, adiponitrile, and chelates, and other organic compounds, especially acrylonitrile, acetone cyanohydrin, and vinylidene cyanide, the latter compounds being intermediates in the manufacture of certain types of synthetic rubbers, plastics, and fibers.
Hydrogen cyanide is produced primarily by the ammoxidation of methane over platinum metals as catalysts. It has also been produced in substantial quantities as a by-product in the ammoxidation of propylene to acrylonitrile. Recent improvements in the catalysts for the acrylonitrile production, however, have resulted in a significant reduction in the quantity of hydrogen cyanide by-product, while, at the same time, demand has increased. As a result, it is highly desirable to provide more efficient catalysts for the production of hydrogen cyanide from readily available raw materials.
Other nitriles of value which may be produced using the catalysts and process of this invention include acetonitrile from ethanol, acrylonitrile from allyl alcohol, and benzonitrile from benzyl alcohol.
2. Description of the Prior Art
Various catalytic processes are known for the oxidation and/or ammoxidation of methanol. Such processes commonly react methanol or a methanol-ammonia mixture with oxygen in the vapor phase in the presence of a catalyst.
Many catalysts are disclosed as suitable in the oxidation and ammoxidation of methanol. In Japanese Kokai patent Sho No. 51[1976]-10200, a metal oxide catalyst consisting of antimony and at least one additional element from iron, cobalt, nickel, manganese, zinc, and uranium, with the atomic ratio of antimony and the additional elements varying from 1/10 to 10/1, preferably 1/2 to 6/1, is disclosed. The catalyst can be used with or without a support, with silica being a preferred support. A catalyst containing tellurium oxide and molybdenum oxide and optionally at least one of the oxides of tungsten, vanadium, chromium, manganese, iron, cobalt, nickel, zinc, tin, bismuth, and antimony is disclosed as suitable for use in a methanol ammoxidation process to produce hydrogen cyanide in Japanese Kokai patent Sho No. 51[1976]-99700. In Japanese Kokai patent Sho No. 53[1978]-149900, a catalyst prepared by spray-drying and calcining a homogeneously mixed solution of silica sol, iron, and molybdenum compounds is disclosed for use in a methanol ammoxidation process. Japanese Kokai patent Sho No. 54[1979]-126698 discloses a catalyst supported on 30-70 wt. % silica represented by the empirical formula: EQU A.sub.a MoBi.sub.b Fe.sub.f Na.sub.n P.sub.p O.sub.q
wherein A is at least one element chosen from among potassium, rubidium, cesium, molybdenum, bismuth, iron, sodium, phosphorus, and oxygen, a, b, f, n, p, and q represent the number of atoms of, respectively, A, bismuth, iron, sodium, phosphorus, and oxygen per one (1) atom of molybdenum, with a being a number within the range of 0-0.05, and b, f, and n are numbers that are determined with the respective formulaes of ##EQU1## In these formulae, X and Y are numbers inside a square wherein the four coordinate points of (0.35, 0.40), (0.35, 0.65), (0.80, 0.40), and (0.80, 0.65) can be connected, Z is a number within the range of 0-0.6, p is a number within the range of 0-0.2, and q is a number taken to satisfy the valences of the elements in the catalyst.
Although the yield and selectivity of the above-described catalysts are generally satisfactory, the commercial utility of a catalyst system is highly dependent upon the cost of the system, the conversion of the reactant(s), the yield of the desired product(s), and the stability of the catalyst during operation. In many cases, a reduction in the cost of a catalyst system on the order of a few cents per pound or a small percent increase in the yield of the desired product represents a tremendous commercial economical advantage. And since it is well known that the economics of manufacturing processes dictate increasingly higher yields and selectivities in the conversion of reactants to products in order to minimize the difficulties attending the purification of the product(s) and handling of large recycle streams, research efforts are continually being made to define new or improved catalyst systems and methods and processes of making new and old catalyst systems to reduce the cost and/or upgrade the activity and selectivity of such catalyst systems. The discovery of the improved catalysts of the present invention is therefore believed to be a decided advance in the state of the art.